The purpose of this study is to explore high school students' environmental literacy and from its result, to suggest ways to reform environmental education. 1047 students from Seoul and Kyeongki province participated in the survey. The questionnaire consisted of four criteria of environmental literacy including knowledge, skill, attitude and behavior. The result was analyzed and the factors which affect high school students environmental literacy were explored. From this result, we made suggestions to improve environmental education as follows. First, environmental education in school should focus on knowledge criterion. Though school environmental education has been helpful for students to build environmental literacy in attitude and behavior criteria, its effect has not been good enough in knowledge criterion. Second, science education can enhance students' environmental literacy. Students who like science best and students who belong to science major classes were reported to possess better understanding in knowledge criterion. Also, students who like life science appeared to have a more positive attitude in environmental literacy. Third, informal education must be considered to form students' environmental literacy. In particular, the effect of mass media is inarguable. Thus, we should find a way to link formal education and informal education to improve environmental education. Fourth, high school students' interest in the environment must be encouraged since it is evident that higher interest would result in better outcome in environmental education.